perspective

Started Sep 19, 2010 | Discussions thread
kenw
Veteran MemberPosts: 4,194Gear list
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Confusion....
In reply to rdk52, Sep 21, 2010

Wow, this thread is reading almost like a DOF thread :).

To sum up what's been mostly right in many responses:

  • Perspective, the relationship of the sizes of objects with respect to the distance from the viewer, is entirely a function of where you or the camera stands and has nothing to do with FL or FOV. The relative sizes of objects will not change regardless of what lens you put on your camera. Perspective only changes if you move the camera.

  • "Normal" FL has nothing to do with the FOV of the human eye which is huge.

  • A "normal" lens is traditionally considered a FL equal to the sensor diagonal. The reason for this is that the "normal" viewing distance for a print is considered to be the length of the print diagonal (you'll step back from big prints, step closer to small ones). As a result, if you take a picture with a lens of FL equal to the sensor diagonal, print it and then place the viewer the distance of the print diagonal away the scene will appear identical to the viewer as if they were standing at the original scene and someone had just put up a wall with a hole in it the size of your print. There is no distortion of perspective in this case. That's what "normal" means in this context, no distortion of perspective in the final print when viewed from a normal distance.

  • A "wide" lens will appear to distort perspective when people view the print from a "normal" distance - the size relationships will be all wrong to them. This is why noses look giant in wide angle portrait and mountains in the distance seem tiny in wide angle landscapes. If we shoved the viewer's face right next to the print the illusion would disappear.

  • A "telephoto" lens will appear to distort perspective for the same reason when viewed from the "normal" distance. This is why space seems to "compress" and why background objects seem giant and looming over the foreground objects. If we force the viewer to stand way back from the print the illusion will disappear.

  • The exact value of "normal" really depends on what you are doing. For LF photographers who print huge wall size prints the reality is that people actually stand much closer than the print diagonal. If you print a small postcard most people will hold it "too far" from them when viewing. In these cases "normal" isn't the usual FL equal to sensor diagonal.

  • Finally, beyond these traditional and technical definitions of "normal" there is the context of the scene itself. Our visual system is very complex and we rarely see and perceive things "accurately". Hence, even when shooting with a "normal" lens and viewing prints from the appropriate "normal" distance the final image may fail to convey what we perceive when we are actually viewing the scene. The most classic example of this is mountains - they almost always seem bigger in person.

The best coverage of this subject is usually in older books on view cameras, they always seem to have the most thorough treatment with the best examples. Actually, if I recall I think the Ansel Adams three book set covers this well someplace (probably in "The Camera").

So for the OP, the 20/1.7 is probably the closest. But don't obsess, as outlined above it depends on a lot of things and anything close to that will give you the desired effect.
--
Ken W

Rebel XT, XTi, Pany G1, LX3, FZ28, Fuji F30, and a lot of 35mm and 4x5 sitting in the closet...

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